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            <span class="post_header_tag" >作者</span>
            <span id="author_id">pg30123</span>
            (<span id="author_nickname">xxxx</span>
            )<span class="post_header_tag">看板</span>
            <span id="board_name">pg30123</span>
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            <span class="post_header_tag">標題</span>
            <span id="post_title">這是一篇文章</span>
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            <span class="post_header_tag">時間</span>
            <span id="post_time">Sun Nov 15 21:00:34 2009</span>
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            <p>
                1. Motivation
                This section is informative.
                RDF/XML [RDF-SYNTAX] provides sufficient flexibility to represent all of the abstract concepts in RDF [RDF-CONCEPTS]. However, it presents a number of challenges; first it is difficult or impossible to validate documents that contain RDF/XML using XML Schemas or DTDs, which therefore makes it difficult to import RDF/XML into other markup languages. Whilst newer schema languages such as RELAX NG [RELAXNG] do provide a way to validate documents that contain arbitrary RDF/XML, it will be a while before they gain wide support.
                Second, even if one could add RDF/XML directly into an XML dialect like XHTML, there would be significant data duplication between the rendered data and the RDF/XML structured data. It would be far better to add RDF to a document without repeating the document's existing data. For example, an XHTML document that explicitly renders its author's name in the text—perhaps as a byline on a news site—should not need to repeat this name for the RDF expression of the same concept: it should be possible to supplement the existing markup in such a way that it can also be interpreted as RDF.
                Another reason for aligning the rendered data with the structured data is that it is highly beneficial to express the web data's structure 'in context'; as users often want to transfer structured data from one application to another, sometimes to or from a non-web-based application, the user experience can be enhanced. For example, information about specific rendered data could be presented to the user via 'right-clicks' on an item of interest.
                In the past, many attributes were 'hard-wired' directly into the markup language to represent specific concepts. For example, in XHTML 1.1 [XHTML11] and HTML [HTML4] there is @cite; the attribute allows an author to add information to a document which is used to indicate the origin of a quote.
                However, these 'hard-wired' attributes make it difficult to define a generic process for extracting metadata from any document since a parser would need to know about each of the special attributes. One motivation for RDFa has been to devise a means by which documents can be augmented with metadata in a general rather than hard-wired manner. This has been achieved by creating a fixed set of attributes and parsing rules, but allowing those attributes to contain properties from any of a number of the growing range of available RDF vocabularies. The values of those properties are in most cases the information that is already in an author's XHTML document.
                RDFa alleviates the pressure on XML format authors to anticipate all the structural requirements users of their format might have, by outlining a new syntax for RDF that relies only on XML attributes. This specification deals specifically with the use of RDFa in XHTML, and defines an RDF mapping for a number of XHTML attributes, but RDFa can be easily imported into other XML-based markup languages.
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            <p>
                2. Syntax Overview
                This section is informative.
                The following examples are intended to help readers who are not familiar with RDFa to quickly get a sense of how it works. For a more thorough introduction, please read the RDFa Primer [RDFaPRIMER].
                For brevity, in the following examples and throughout this document, assume that the following vocabulary prefixes have been defined:
                biblio: 	http://example.org/biblio/0.1
                cc: 	http://creativecommons.org/ns#
                dbp: 	http://dbpedia.org/property/
                dbr: 	http://dbpedia.org/resource/
                dc: 	http://purl.org/dc/elements/1.1/
                ex: 	http://example.org/
                foaf: 	http://xmlns.com/foaf/0.1/
                rdf: 	http://www.w3.org/1999/02/22-rdf-syntax-ns#
                rdfs: 	http://www.w3.org/2000/01/rdf-schema#
                taxo: 	http://purl.org/rss/1.0/modules/taxonomy/
                xhv: 	http://www.w3.org/1999/xhtml/vocab#
                xsd: 	http://www.w3.org/2001/XMLSchema#
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            <p>
                2.1. The RDFa Attributes
                RDFa in XHTML makes use of a number of XHTML attributes, as well as providing a few new ones. Attributes that already exist in XHTML will have the same meaning as in XHTML, although their syntax may be slightly modified. For example, in XHTML, @rel already defines the relationship between one document and another. However, in XHTML there is no clear way to add new values; RDFa sets out to explicitly solve this problem, and does so by allowing URIs as values. It also introduces the idea of 'compact URIs'—referred to as CURIEs in this document—which allow a full URI value to be expressed succinctly.
                The XHTML attributes that are relevant are:
                @rel
                a whitespace separated list of CURIEs, used for expressing relationships between two resources ('predicates' in RDF terminology);
                @rev
                a whitespace separated list of CURIEs, used for expressing reverse relationships between two resources (also 'predicates');
                @content
                a string, for supplying machine-readable content for a literal (a 'plain literal object', in RDF terminology);
                @href
                a URI for expressing the partner resource of a relationship (a 'resource object', in RDF terminology);
                @src
                a URI for expressing the partner resource of a relationship when the resource is embedded (also a 'resource object').
                The new—RDFa-specific—attributes are:
                @about
                a URIorSafeCURIE, used for stating what the data is about (a 'subject' in RDF terminology);
                @property
                a whitespace separated list of CURIEs, used for expressing relationships between a subject and some literal text (also a 'predicate');
                @resource
                a URIorSafeCURIE for expressing the partner resource of a relationship that is not intended to be 'clickable' (also an 'object');
                @datatype
                a CURIE representing a datatype, to express the datatype of a literal;
                @typeof
                a whitespace separated list of CURIEs that indicate the RDF type(s) to associate with a subject.
                For a normative definition of these attributes see the XHTML Metainformation Attributes Module.
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